is a global variable whose value, if set, is applied to every input expression.


$Pre
is a global variable whose value, if set, is applied to every input expression.
Details

- Unless $Pre is assigned to be a function which holds its arguments unevaluated, input expressions will be evaluated before $Pre is applied, so the effect of $Pre will be the same as $Post.
- $Pre is applied to expressions, while $PreRead is applied to strings which have not yet been parsed into expressions.
Tech Notes
Related Guides
History
Introduced in 1988 (1.0)
Text
Wolfram Research (1988), $Pre, Wolfram Language function, https://reference.wolfram.com/language/ref/$Pre.html.
CMS
Wolfram Language. 1988. "$Pre." Wolfram Language & System Documentation Center. Wolfram Research. https://reference.wolfram.com/language/ref/$Pre.html.
APA
Wolfram Language. (1988). $Pre. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/$Pre.html
BibTeX
@misc{reference.wolfram_2025_$pre, author="Wolfram Research", title="{$Pre}", year="1988", howpublished="\url{https://reference.wolfram.com/language/ref/$Pre.html}", note=[Accessed: 15-August-2025]}
BibLaTeX
@online{reference.wolfram_2025_$pre, organization={Wolfram Research}, title={$Pre}, year={1988}, url={https://reference.wolfram.com/language/ref/$Pre.html}, note=[Accessed: 15-August-2025]}